1. Field of the Invention
The present invention relates to a device used to retain a placard within a placard holder.
2. Background Art
Placards are used in many situations to provide information to a reader about a particular material or device with which the placard is spatially related. The placard is usually positioned in such a manner that it is nearby or affixed to the package or container holding the thing described on the placard. Often, placards are placed within a holding device that is secured nearby, or on, the package or container. The advantage of the holding device is that it allows a placard to be changed when the contents of the associated package or container are changed. This is particularly useful where the placard holder is affixed to a refillable container such as a drum, railcar, shipping container, or the like.
Placards are also used as a source of information identifying the type of hazard a hazardous material in shipment may pose. This type of placard forms a component of an international system of hazard communication. Prominent display of the placard on shipping containers functions to immediately warn responders, handlers and bystanders that hazards are present and that caution should be taken when interacting with the container's contents. Therefore, it is critical that when such a placard is placed on a container that it remain firmly attached to the container throughout the time that the hazardous material is present.
Due to the standardized size and format of many hazardous material placards, the holders with which they are used must be designed so they do not obscure the information being displayed on the placard. This limitation restricts the available upper surface area of the placard that may be contacted by the placard holder for the purpose of restraining the placard within the holder. The placard holder is often comprised of a back frame member attached to the transport container and a front frame member having a flat surface portion enclosing an open window area. Such a placard holder is described in U.S. Pat. No. 4,229,891 to Keller, the disclosure of which is fully incorporated by this reference. In other prior art devices, the placard holder is as described in Keller, but without the locking arm, the outer lip, the locking tabs, and the ridges. Still further alternative prior art devices, the placard holder is as described in Keller, but the back frame is a surface of the vehicle/container such that the placard holder is permanently affixed to the vehicle/container. In yet further alternative prior art devices, the placard holder is as described in Keller, but without the locking arm, the outer lip, the locking tabs, and the ridges; and the back frame is a surface of the vehicle/container such that the placard holder is permanently affixed to the vehicle/container. The front and back frame members are usually peripherally bound by a spacing member that creates a placard pocket between the front and back frame members. At least some part of the periphery is left unbounded so as to allow access to the placard pocket. To facilitate ease of insertion and removal of the placards, the tolerances to which the placard holders are manufactured are large, usually resulting in excess space between the surfaces and edges of the placard and the placard holder.
However, when such placard holders are used on surfaces subject to atmospheric disturbances, whether natural or artificial, several problems have been identified. The atmospheric disturbance may be weather related, but is more often the result of the method by which the container on which the placard holder is placed is transported. For example, a tractor trailer vehicle pulling a tanker containing hydrochloric acid (“HCl”) would be required to have hazardous material placards on both ends and both sides of the tanker identifying the contained material as HCl. However, when moving down the road at speeds often exceeding forty miles per hour (40 mph), the placards are subjected to winds at or near the speed at which the vehicle is traveling. This often results in air flow beneath the placard, causing it to shift within the placard holder. Even worse, the placard can lift away from the vehicle, become bent or broken, or otherwise damaged, thus limiting its ability to effectively convey the information contained on it.
What is needed is a placard holder that will restrict the movement of the placard within the placard holder, so that the placard substantially maintains its original position, no matter the atmospheric conditions to which it is subject.